Putting vinyl siding on a Chicago bungalow is like putting ketchup on a Chicago hot dog.

It’s not illegal, but it frays the fabric of our city.

Chicago’s neighborhoods are graced with more than 80,000 bungalows, most of them built between 1910 and 1940.

Anybody who grew up here knows what it’s supposed to look like: face brick with stone trim, 1½ stories atop a basement, longer than wide, a low-pitched roof with an overhang, and an offset front door.

Accept no substitutes. A brick bungalow is as Chicago as Wrigley Field.

EDITORIAL

But as Yvonne Kim of the Sun-Times reported this week, “pop top” expansions — enlarging and squaring off the second floor — are turning many classic Chicago bungalows into drab vinyl rectangles. Preservationists are shuddering, and so are we.

A bungalow is hardly a bungalow once a pre-fab tool shed is plopped down on top.

City Hall and the Chicago Bungalow Association are encouraging bungalow owners to take a pass on “pop tops” and renovate with an eye toward preserving their homes’ essential characters.

Last month, the association began working with the American Institute of Architects to provide homeowners with plans showing how bungalows can be tastefully renovated, adding space without upending tradition.

Bungalows were Chicago’s original “starter” houses. They always were meant to be expandable. That was a selling point. Families of modest means could scrape together a down payment and move in, then add space as their needs and income grew.

And there have always been clever ways to add that space without compromising character.

Drive through the Bungalow Belt and you know where you are — Chicago. It’s a feeling as homey as a bungalow itself, and one worth preserving.

Brick bungalows line the 4700 block of North Lowell Avenue in 2010. | John H. White/Chicago Sun-Times

Send letters to letters@suntimes.com.